In recent years, miniaturization and weight reduction of portable devices such as a mobile phone, a portable audio player, and a PDA (Personal Digital Assistant) have been remarkably improved. The miniaturization of the battery to be mounted has played a part of the technology improvement.
As a small battery, a battery in which a flat winding-type electrode body is housed a film-like sheath material with high flexibility in molding has been proposed (for example, see PTL 1). By using such a film-like sheath material, cell design appropriate for portable electronic devices to be diversified is possible. In recent years, miniaturization of batteries using such a sheath material is desired.